The present invention relates to an imaging apparatus and a subject moving apparatus.
An imaging apparatus, such as an X-ray CT (Computed Tomography) apparatus, acquires raw data by scanning a subject accommodated in an image pickup space and generates an image of the subject on the basis of the raw data.
In an X-ray CT apparatus, for instance, an X-ray tube and an X-ray detector are so arranged on a scanning gantry to place an image pickup space between them, and a subject moving apparatus moves a subject supported by a cradle unit into the image pickup space. And when helical scanning is to be performed for instance, the subject moving apparatus, after starting up the cradle unit by accelerating it at a prescribed rate of acceleration, slides it at a constant speed. It drives the cradle unit in this way, afterwards decelerates it at a prescribed rate of deceleration, and stops the unit. And when, for instance, the cradle unit is sliding at a constant speed in the image pickup space, the X-ray tube and the X-ray detector rotate around the subject supported by the cradle unit, and as X-rays are radiated in viewing directions around the subject, the X-ray detector acquires raw data in each viewing direction. And on the basis of the raw data in each viewing direction, sectional images of the subject in desired slicing positions and slicing thickness are generated by reconstruction (see JP-A No. 2004-173756).
Besides that, in the X-ray CT apparatus, the scanning gantry so moves the subject toward the cradle unit supporting it as to accommodate the subject in the image pickup space. And, in a similar way, X-rays are radiated in viewing directions around the subject, and the X-ray detector, acquiring raw data in each viewing direction, generates sectional images of the subject by reconstruction (see JP-A No. 2003-153889).
In driving the cradle unit or the scanning gantry as described above, a stepping motor is used for instance. In this case, the driving of the stepping motor is so controlled as to keep the absolute value of the torque constant irrespective of its number of revolutions.
In recent years, however, as the moving speed of the cradle unit or the scanning gantry is increased to realize a higher efficiency of imaging by increasing the scanning speed or the range of scanning, scanning may also be executed when its driving is accelerated or decelerated.
However, in such a case, such a trouble as desynchronization of the stepping motor which drives the cradle unit or the scanning gantry may occur, making it difficult to drive the cradle unit or the scanning gantry, and therefore required compatibility with the higher scanning speed or the expanded scanning range is sometime impossible to be achieved. For this reason, it is sometimes difficult according to the prior art to accomplish imaging efficiently. Especially when the cradle unit or the scanning gantry is to be driven under acceleration from an unmoving state, the aforementioned trouble could be more conspicuous.